1. Field of the Invention
The present invention concerns an improved method for producing elasticized articles at high speed.
The present invention has further relation to such a method wherein an elastically contractible element is applied while in a substantially untensioned, molecularly oriented, heat unstable condition, and is thereafter subjected to an external stimulus, such as heat, to impart shirring to the article.
The present invention has particular relation to an improved method for forming elasticized articles wherein the article is comprised of two or more layers of material, including at least one elastically contractible polymeric element secured thereto in a substantially untensioned, molecularly oriented, heat unstable condition, said article thereafter being cut along a non-linear line of serverance at a point coinciding with said elastically contractible element so as to divide said elastically contractible element into at least two portions which will, upon subsequent heat treatment, cause shirring and elasticization of each of the non-linear severed edges thus produced.
Finally, the present invention has relation to an article exhibiting a non-linear, shirred, elasticized edge formed by said method.
2. Background Art
Infants (and other incontinents) wear disposable diapers to receive and contain urine, feces, and other body fluids. Disposable diapers function both to contain the discharged materials and to isolate these materials from the body of the wearer and from the wearer's surroundings. Modern embodiments of disposable diapers frequently perform these tasks in a manner superior to that of traditional cloth diapers.
Disposable diapers normally comprise three elements: a liquid permeable topsheet designed to be placed next to the wearer's skin; a liquid impermeable backsheet which forms, in use, the outer surface of the diaper; and an absorbent element interposed between the topsheet and the backsheet.
The topsheet is frequently a hydrophobic non-woven fabric which is readily permeable to fluid. Its hydrophobicity tends to cause the surface in contact with the wearer's skin to be dry and the skin to be protected from fluids absorbed within the absorbent element.
The absorbent element receives and retains fluids which pass through the topsheet. It normally comprises a batt of airlaid wood pulp fibers.
The backsheet functions to contain fluids within the absorbent element, thereby protecting the wearer's outer garments and other surfaces from soiling by these fluids. Backsheets are commonly formed of fluid impermeable materials such as polyethylene film.
Disposable diapers having many different basic designs are known in the art. The prior art patents hereinafter cited in the Background Art portion of the present specification, all of which are hereby incorporated herein by reference, are exemplary of such structures.
Duncan and Baker in U.S. Pat. No. Re. 26,151, issued Jan. 31. 1967, descirbe and claim a disposable diaper which has achieved wide acceptance and commercial success. Buell, in U.S. Pat. No. 3,860,003, issued Jan. 14, 1975 and hereby incorporated herein by reference, describes and claims another disposable diaper which, too, has achieved wide acceptance and commercial success. The diaper taught by Buell differs from that taught by Duncan and Baker in many respects, not the least of which is the provision in the Buell diaper of elasticized (or contractible) leg cuffs. Strickland and Visscher in U.S. Pat. No. 4,253,461, issued on Mar. 3, 1981, describe and claim another form of disposable diaper, sometimes referred to as an incontinent brief, intended to be worn by adults.
Mesek et al. in U.S. Pat. No. 4,324,245, issued Apr. 13, 1982; Pieniak et al. in U.S. Pat. No. 4,337,771, issued July 6, 1982; Mesek et al. in U.S. Pat. No. 4,352,355, issued Oct. 5, 1982 and Sciaraffa et al. in U.S. Pat. No. 4,381,781, issued May 3, 1983, describe disposable diapers having elasticized cuffs and elasticized (or contractible) waistbands.
Imparting elasticization to discrete articles has taken various forms. One particularly preferred method for continuously attaching discrete stretched elastic strands to predetermined isolated portions of disposable absorbent products is disclosed in U.S. Pat. No. 4,081,301 issued to Buell on Mar. 28, 1978 and hereby incorporated herein by reference. The inventive concept disclosed in the Buell patent, in a broad sense, relates to the continuous adherence of discrete lengths of stretched elastic to predetermined portions of a continuously moving web at relatively high operating speeds and thereafter severing the elastic in the unadhered areas to produce elasticized structures having discrete strands of elastic adhered thereto at predetermined locations along their length. In a particularly preferred embodiment, the aforementioned process is utilized to apply discrete elastic legbands to a disposable diaper structure to provide improved containment and fit therein.
An alternative apparatus and method for attaching elastic strips during the manufacture of elastic leg disposable diapers is disclosed in U.S. Pat. No. 4,261,782 issued to Teed on Apr. 14, 1981. According to the process disclosed in the Teed patent, the elastic strips are fed in the direction of web travel and are alternately stretched and relaxed during the attachment process.
Still other approaches to providing shirred, elastic, flexible articles involve the application of an oriented elastic material to the article to be elasticized in an untensionsed state and thereafter subjecting the oriented elastic material to heat to cause shrinkage and consequently shirring by restoring the material to its unoriented and elastic state. Exemplary of such processes are those shown in U.S. Pat. No. 3,912,565 issued to Koch et al. on Oct. 14, 1975, U.S. Pat. No. 3,639,917 issued to Althouse on Feb. 8, 1972 and U.S. Pat. No. 3,819,401 issued to Massengale et al. on June 25, 1974.
Koch discloses a method wherein a thin layer of flexible polyurethane material, which is heat shrinkable in the desired direction of article shirring, is disposed in direct contact with at least one side of a flexible sheet material and attached thereto without any significant shrinkage or other distortion of such layer. Subsequently, the layer of polyurethane material is heated to cause shrinkage thereof, whereby the sheet material attached thereto is shirred. The thermoplastic polyurethane resins employed by Koch may be shaped into the desired layer by conventional procedures, as for example by extruding in a molten condition as a continuous stream, followed by rapid quenching of such stream as on a chill roll or in a bath of cool water or other liquid. The layer of polyurethane material thus formed may be collected for subsequent processing at a later stage or, in continuous operations, may be uniaxially stretched directly after its formation. This may be accomplished as by stretching such layer of polyurethane material longitudinally between spaced pairs of differential speed rolls; that is, with one such pair of rolls being rotated at a more rapid speed than the other of such pair of rolls. The uniaxially oriented layer of polyurethane material is preferably heat set by being brought to a temperature slightly above its second order phase transition temperature, permitted a limited relaxation, and then cooled to the temperature of the ambient atmosphere. Once cooled the layer is dimensionally stable. In the example disclosed in the Koch patent, lengths of the heat shrinkable, heat set tape created by the foregoing method are removed from a supply roll and are placed in direct contact with a garment body adjacent to the openings to be elasticized. The attached tape lengths are then heated to shrink the same and cause the portions of the article body to which they are attached to shirr or gather.
Similar approaches utilizing other elastomeric materials are disclosed in the aforementioned patents to Althouse and Massengale et al.
In order to facilitate economical production, and hence disposability, of articles such as disposable diapers, incontinent briefs and the like, it is essential that the means of elasticizing these articles be capable of high speed and great reliability. Since articles such as disposable diapers are typically produced by forming a continuous web of the articles interconnected to one another at their adjacent waistband portions, processes such as those disclosed in the aforementioned U.S. Pat. No. 4,081,301 to Buell have functioned well in the application of stretched elastic bands in a direction generally parallel to the direction of web travel to form elasticized leg cuffs.
However, when it is desired to apply an elastic element intended to cause shirring of the finished article in a direction generally perpendicular to the direction of web travel at high speed while the web is moving, the method generally disclosed in the commonly assigned, copending patent application of L. Richard Chapman and Wayne I. Fanta, Ser. No. 476,733, filed Mar. 18, 1983 and entitled "CONTINUOUS METHOD FOR ELASTICIZING DISCRETE ARTICLES CUT FROM A MOVING WEB IN A DIRECTION PERPENDICULAR TO WEB TRAVEL" is particularly preferred. Specifically, the aforementioned application of Chapman et al. discloses a method for continuously elasticizing articles such as disposable diapers, incontinent briefs, and the like by securing an elastically contractible element to a moving, interconnected web of said articles, said elastically contractible element causing discrete articles cut from the web to shirr in a direction substantially perpendicular to the direction of web travel. Said elastically contractible element is preferably applied to said moving web while in a substantially untensioned, molecularly oriented, heat unstable condition, and is thereafter subjected to an external stimulus, such as heat which causes shrinkage of the elastically contractible element in a direction substantially perpendicular to the direction of web travel and shirring of the diaper waistband. The application of heat is preferably done after the discrete articles have been cut from the web and are in a substantially untensioned state to impart shirring.
Quite unexpectedly, it has been found that when the method generally disclosed in the aforementioned patent application of Chapman et al. is operated at high speed using a crush type cutter, e.g., a rotating cylinder having one or more radially extending blades mounted at its periphery operating against a hard surfaced anvil roll, plastic flow of certain of the polymeric materials comprising the article, including the elastically contractible element which serves as the waistband, results during the cutting operation which separates the individual articles from the continuous web. The resultant plastic flow causes fusing of the elements comprising the diaper at the severed edges of the structure. The effect becomes most pronounced in situations where the web is folded into a predetermined cross-section, such as a c-fold or an e-fold, prior to severance, since more layers of material are fused to one another, thereby creating a stiffened edge at the point of severance. It has further been found that when the fused, severed edges are formed by means of a linear cut oriented substantially perpendicular to the direction of web travel, the application of an external stimulus, such as heat, to impart shrinkage of the heat unstable, elastically contractible element is rendered to a degree ineffective. This is believed due to the resistance imparted by the stiffened, fused, edges formed during the cutting operation.
Similar results are observed when cutting operations employing heat energy, e.g., a laser beam, are employed to sever discrete articles from the web of interconnected articles.
Accordingly, it is an object of the present invention to produce a disposable diaper or other article incorporating an elastically contractible element such as a waistband which undergoes a joint severance operation with one or more of the layers comprising the article, yet which, upon the application of an external stimulus such as heat, will return to its molecularly unoriented, heat stable state and thereby impart both shirring and elasticization to the severed edge of the article in a direction substantially parallel to the overall orientation of the line of severance.
It is a further object of the present invention to provide a method of severing discrete diapers or other articles from a continuous web of said diapers or articles such that the stiff columnar effect created at the severed edge by fusing of the layers comprising the diaper or article to one another is minimized.